Tandem welding shielding gases

ABSTRACT

The invention relates to a shielding gas for gas shielded metal-arc welding or gas shielded metal-arc soldering with multiple (in particular 2) wire electrodes. According to the invention, it contains helium.

[0001] The invention relates to shielding gases especially suitable forgas for gas metal-arc welding with multiple wire electrodes, especiallywith two wire electrodes.

[0002] Gas metal-are welding (MSG) with an electrode is a standardizedprocess whose properties are described with a score of 2430 according tothe draft of DIN ISO 857 or 13 according to ISO 4063.

[0003] Two gas shielded metal-arc welding processes with multiple wireelectrodes are known from the technical literature, e.g., the periodical“Der Praktiker” No. 1, 2000, pages 18 and 19. The gas shieldedmetal-arc-double-wire process is a single-head welding process with twoelectrodes under a shielding gas and a common voltage source. Thesimultaneous melting of the two wire electrodes ensures higher meltyields and welding speeds compared to the single-wire process. Thismakes possible an increase in productivity. The other process is theso-called tandem-welding process. The latter offers a better monitoringof the process.

[0004] The present invention relates to “tandem welding or soldering”,which is defined in “Merkblatt DSV 0909-1” on page 4 as a process withtwo consumable metal electrodes in one common melting bath. The twoelectrodes can have different potentials and different electrode feedingspeeds FIG. 11 shows two power sources and two wire feeding motors(Drahtvorschube)). Tandem welding is also shown in U.S. Pat. No.4,806,735 Ditschun et al. It is different from “Doppeldrahtschweiβen”(FIG. 10 ) where there is only one power source and one potential forboth electrodes (see also JP 85-137742/23).

[0005] The processes of welding and soldering with arcs under ashielding gas are distinguished as follows: During welding, a weld pooldevelops from molten material and—if used—from the welding rod or thewelding rods. During gas shielded metal-arc soldering, the materialmelts only slightly or not at all, however. The two processes aresimilar in many respects but special, process-specific problems alsooccur.

[0006] The spatial proximity of the two arcs causes them to influenceeach other. Electric and electromagnetic fields and forces are at workthat influence the metal transition in the arc. Unless the parametersare optimally selected, these forces result in process disruptions,spattering, and, in the extreme case, in weld defects.

[0007] Attempts are now made to address these problems via wiredistance, contact pipe distance or pulse parameters.

[0008] One object of this invention is to provide mixtures of gasesespecially suitable as a tandem-welding shielding gas or a tandemsoldering shielding gas that prevents or reduces these problems.

[0009] Another object of this inventions is to provide tandem weldingand soldering processes using the shielding gases.

[0010] Upon further study of this invention, other objects andadvantages will become apparent.

[0011] To achieve these objects, there are provided several gases setforth in the claims, all of which contain helium. To use helium in ashielding gas is known for normal welding with one electrode (Marks'Standard Handbook) or for Doppeldrahtschweiβen (JP 85-137742/23) or forwelding with two melding baths (JP 54071744) U.S. Pat. No. 6,207,929wherein the two electrodes are separated and far from each other.However, heretofore, there was no suggestion to use helium as ashielding gas for the type of tandem welding or soldering of thisinvention, using a single bath.

[0012] The admixture of helium in the shielding gas according to theinvention results in an arc tightening and reduces the above-mentionedelectromagnetic forces and their effects. Helium primarily replaces theless expensive argon; the higher ionization potential of helium relativeto that of argon produces a better arc stability. Helium thus acts as anelectric resistor. By the higher ionization potential, the volume ofionized gas that surrounds the two arcs is reduced. Moreover, at aconstant voltage, helium produces a shorter arc. In the case of a shortarc, the path that the drop must cover from the melting electrodes tothe weld pool is shortened. Since on this segment, however, the dangerexists that the drop will be deflected from its path by the field forcethat the second arc causes and land as a spatter on the material surfaceor the weld, helium effectively reduces spattering.

[0013] To date, two-component mixtures that consist of argon and CO₂ orargon and O₂ were recommended for the MAG-welding of steels, such as,e.g., structural steels and high-alloy steels (alloy steels andnickel-based materials). To a certain extent, CO₂ also produces arctightening, but cannot be admixed at will, since in larger amounts, ithampers and strongly oxidizes the drop detachment. The helium that isproposed according to the invention is inert, however.

[0014] In the following discussion and in the claims, all percentagesare by volume.

[0015] For unalloyed and low-alloy steels, a helium proportion ofbetween 15% and 75% has proven especially advantageous. The heliumproportion as well as the CO₂ proportion, which is in the range of 2% to20%, or the O₂ proportion, which is between 1% and 6%, produce good weldappearance and high-quality compounds at high welding or solderingspeeds.

[0016] In the case of high-alloy materials, in which the nickel-basedmaterials and the high-alloy steels are included, helium mixtures withrelatively low additions of CO₂ or O₂ show the best welding results.Here, helium also provides for a high arc stability and reduces theformation of spatters. A helium proportion of 10% to 99.95% or 99.97%,depending on the other components, is preferred. Especially preferred inthis case is the range between 20% and 70%. By adding 0.05% to 5% CO₂ or0.03% to 4% O₂, the advantages of these active gases result for example,in arc tightening. Whereas these active gases exhibit drawbacks, whichinclude for example, the oxidation of the workpiece, the disadvantagesare far outweighed by the advantages are still insignificant.

[0017] For MAG welding with two wire electrodes, the gas mixtures withthe compositions of the claims have proven advantageous. DuringMIG-two-electrode welding, e.g., of aluminum materials, now primarilyargon is used. Also here the helium admixture according to the inventionacts as in the MAG welding.

[0018] The helium addition according to the invention can also be usedwith the newer “doped” gases, which contain small admixture componentsof N₂, O₂, NO or combinations of these gases. The admixtures are in theppm range in most cases. For welding and soldering of aluminum andaluminum alloys, in particular a mixture that consists of argon andhelium, with a helium proportion of 10% to 75%, preferably 15% to 50%,especially preferably 20% to 30%, is suitable. In the case of aluminummaterials, the high heat conductivity of helium is of specialimportance, since the latter provides for a good heat input at thewelding site—despite the high heat conductivity of aluminum.

[0019] The adding of micro-admixtures improves the weld appearance andthe weld quality significantly. As doping gases, N₂, O₂, NO orcombinations of these gases are advantageously used. The doping iscarried out in this case at 100-5000 vpm, preferably at 150-1000 vpm.The helium proportion provides for the above-mentioned advantages in thecase of aluminum and is between 10% and 75%, preferably 15 and 50%,especially preferably 20% and 30%. Doping with 250 to 500 vpm of O₂ hasproven especially effective.

[0020] In further development of the invention, hydrogen is added as anadditional component to the shielding gas according to the invention. Inthis case, the range of concentration of hydrogen is between 0.1% and 8%is preferred. The H₂ proportion in the shielding gas produces anadditional stabilization of the arc and a further improvement of theheat input. Also, the wetting behavior of the weld pool is furtherincreased by the hydrogen. Depending on materials, however, at this timehydrogen-containing gases are recommended only for some nickel-basedmaterials, since other materials, such as, e.g., aluminum alloys orsteels with a ferrite proportion, do not tolerate any hydrogen.

[0021] The invention offers the following advantages:

[0022] Increased process stability

[0023] Splatter reduction

[0024] Reduction of the sensitivity of the process to disruption

[0025] Better weld shape by better weld flow

[0026] Reduction of oxidation with MAG

[0027] Reduction of pores with MIG

[0028] Better penetration with MIG.

[0029] (“MIG” is an asserted trademark of Lincoln Electric Company ofCleveland, Ohio, as stated in the brochure of Lincoln Electric “TandemMIG Process” E10.60 4/99.)

[0030] (“MAG” is an abbreviation for gas metal-arc welding wherein thegas is an active gas as compared to an inert gas, e.g. CO₂.)

[0031] Primary users of the technology are the motor vehicle industry,the automobile industry, the railroad industry and suppliers as well asthe machine-building and container industries.

[0032] The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

[0033] The entire disclosures of all applications, patents andpublications, cited above or below, and of corresponding Germanapplication No. 10122869.4, filed May 11, 2001 is hereby incorporated byreference.

[0034] From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention and, withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

[0035] In the following claims, “low-alloy steels”, “high-alloy steels”and “aluminum materials” are defined as:

[0036] A low-alloy steel has less than 5% by weight of any non-ferrousalloying element.

[0037] A high-alloy steel has more than 5% by weight of non-ferrousalloying elements, e.g. Cr, Mo, Ni.

[0038] An aluminum material contains aluminum as the main component,e.g. at least 50% by weight of aluminum.

1. Shielding gas for the gas shielded metal-arc welding or gas shieldedmetal-arc soldering with multiple (in particular 2) wire electrodes,characterized in that it contains helium.
 2. Shielding gas according toclaim 1, characterized by the following components: CO₂: 0.05% to 25%He: 10%-99.95%, preferably 10%-75% Ar: remainder.
 3. Shielding gasaccording to claim 1, characterized by the following components: O₂:0.03%-10% He: 10% to 99.97%, preferably 10%-75% Ar: remainder. 4.Shielding gas according to claim 1, wherein it contains 100% helium. 5.Shielding gas for welding or soldering unalloyed and low-alloy steelsaccording to claim 1, characterized by the following components: CO₂:2%-20% He: 15%-75%, preferably 20%-50% Ar: remainder.
 6. Shielding gasfor welding or soldering unalloyed and low-alloy steels according toclaim 1, characterized by the following components: O₂: 1%-6% He:15%-75%, preferably 20%-50% Ar: remainder.
 7. Shielding gas for thewelding or soldering of high-alloy steels according to claim 1,characterized by the following components: CO₂: 0.05%-5% He: 10% to99.95%, preferably 20%-70% Ar: remainder.
 8. Shielding gas for thewelding or soldering of high-alloy steels according to claim 1,characterized by the following components: O₂: 0.03%-4% He: 10%-99.97%,preferably 20%-70% Ar: remainder.
 9. Shielding gas for the welding orsoldering of aluminum materials according to claim 1, characterized bythe following components: He: 10%-75%, preferably 15%-50%, especiallypreferably 20%-30% Ar: remainder.
 10. Shielding gas for the welding orsoldering of aluminum materials according to claim 1, characterized byadmixtures of N₂, O₂, NO or combinations of these gases as doping gas.11. Shielding gas according to claim 10, characterized by the followingcomponents: Doping gas (N₂, O₂ and/or NO) 100-5000 vpm, preferably150-1000 vpm He: remainder.
 12. Shielding gas according to claim 10,characterized by the following components: Doping gas (N₂, O₂ and/or NO)100-5000 vpm, preferably 150-1000 vpm He: 10%-75%, preferably 15-50%,especially preferably 20%-30% Ar: remainder.
 13. Shielding gas accordingto claim 12, characterized by the following components: Doping gas 0 ₂250-500 vpm He: 10%-75%, preferably 15-50%, especially preferably20%-30% Ar: remainder.
 14. Shielding gas according to one of claims 1 to13, wherein the shielding gas contains hydrogen, preferably 0.1% to 8%H₂, as an additional component.
 15. Gas shielded metal-arc weldingprocess or gas shielded metal-arc soldering process with multipleelectrodes, characterized by the use of one of the gases of theabove-mentioned claims.